Time comparison in Prolog

Question

Say I have a structure time with the format time(hour, minute). How would I go about writing a rule to compare them? Something along the lines of compareTime(time1,time2) that returns yes if time1 is strictly before time2.

I am just starting out with Prolog after years of working with C, and the entire language is very very confusing to me.

Answer 1

The standard compare/3 predicate already does what you want:

?- compare(O, time(1,1), time(1,1)).
O = (=).

?- compare(O, time(1,1), time(1,2)).
O = (<).

?- compare(O, time(1,3), time(1,2)).
O = (>).

?- compare(O, time(1,3), time(2,2)).
O = (<).

?- compare(O, time(3,2), time(2,2)).
O = (>).

so...

earlier(T1, T2) :- compare((<), T1, T2).